Spray drying



P" 1927 A. a. JONES SPRAY DRYING Filed June 13, 19:35

A TTORNE Y3 Patented Apr. 12, 1927.

- UNITED STATES PATENT OFFICE.

ARTHUR 3. JONES, OF PLAINFIELD, NEW JERSEY, ASSIGNOR *TO INDUSTRIALABSO- CIATES, INCORPORATED, OF NEW YORK, N. Y., A CORPORATION OF NEWYORK,

SPRAY DRYING.

A p'uoamn filed June 1a, 1920. snarno. 116,980.

My invention relates to spray dr ing, and is applicable to the recoveryof so ids from organic and inorganic fluids, sem -fluids, plastics,etc., capa le of dispersion in comminuted condition by centrifugal forceor otherwise. The object of my invention is to provide improvedapparatus and operation for convection current systems, and by which theavailable heat unlts of the convection current are more completelyexhausted in useful work before the gas leaves the dr ing chamber.

In the accompanying drawing- Fig. 1 is a vertical section, through amore or less diagrammatically illustrated layout of apparatus embodyingmy invention in one form. 1

Referringto the more or less diagrammatic drawing, I have indicated anouter, closed casing or shell 1, which surrounds but is spaced from asheet metal cylinder 2 arranged on a vertical axis and constituting thedryin chamber proper. The intervening space hetween the casingandcylinder is horizontally divided by partition 3 into upper and lowercompartments 4 and 5 respectively. Heated air or other gas is admittedto the u per compartment 4 through port 6, passes t ence through thedrying chamber 2, escapes from the bottom of the latter to compartment 5and exits therefrom through port 7.

Arranged centrally and adjacent the upper margin of the dryin chamber isa centrifugal spray unit 8 w ich receives from feed 9 the fluid orplastic material to be dried, and dis erses the same in a surroundingnebula. n the subjoined claims I employ the word fluid in a sense broadenough to include any material, whether a liquid or a plastic solid ormud which is susceptible of dispersal in the form of a very fine sprayor nebula.

In apparatus of this general type, as heretofore constructed, the upperen of the drying chamber 2 has been open throughout its completediameter. The incoming hot gases have been distributed consequently overthe entire cross sectional area of the cylinder, and their downwardflowthrough the latter has been substantially uniform at all points.

.This arrangement lacks efficiency, since the nebula is most dense inthe immediate neighborhood of the spray unit'S and the hot gas passingthrough this portion of the nebula absorbs more moisture than thesurrounding or peripheral portion of the gas current. Thelatter thusgives up a lessproportion of its useful heat and leaves the dryingchamher without absorbing all the moisture which it is capable ofcarrying at its exit temperature.

I have found that this waste of useful heat is greatly reduced, if theupper end of the drying chamber is to a large extent closed by a head10, preferably inwardly dished as shown, and having acentral inlet port11. The precise area of this port may vary-but I prefer that its'areashall be approximately four or five times that (if the spray unit 8,which is centrally located with respect thereto.

s a result of this construction, the hot gas enters the drying chamberparallel to the axis of the spray unit and is concentrated on thedispersed nebula in its densest area. The force of the impinging currentof gas'deflects the nebula downward and thus causes the heavierparticles thereof to travel a downward and outward path at an an triugal spray unit. The length of this downwardly deflected path from thespray unit 8 to'thewall of the dryingchamber is materially greater thanthe ath to the wall in the plane of rotation of t e unit 8;Consequently, the particles are subjected for a greater length of timeto the desiccating action of the gaseous current. a

A second important result of the construction is the establishment of anannular upwardly flowing gaseous current which surrounds a centraldownwardly flowing current in the drying chamber. This is due not onlyto the usualtendency'to eddy or whirlpool formation incident to theprojection of a jet or stream of gas into a larger relatively quiet bodythereof, but also to other influences, First, the portion of the gaswhich contacts with the nebula in its densest area, very rapidly givesup its heat in the absorption of molsture from the nebula, and istherefore chilled to a greater extent than the surrounding portion ofthe gas which permeates the outer area of the nebula. This central,chilled and moisture laden portion of the gas current tends to sink, bygravity, more rapidly than the gle to the plane of rotation of the cen-=outer, less chilled, less moisture laden, portion thereof and forms inconsequence a central downwardly moving column of as, practicallysaturated with moisture. he surrounding less saturated gas, at hlghertemperature, tends to rise and to form an upwardly flowing current.Second, the portion of the dr ing chamber Wall which lies above the diapiragm 3, and also the head 10 of the drying chamber, are heated by theincoming hot gas in the compartment 4. The peripheral unsaturatedportion of the gas in the drying chamber is heated by the wall of thedrying chamber and tends to risetoward the head 10 of the dryingchamber, where it is further heated. Third, the jet efl'ect of the gasentering the drying chamber through port '11, exerts a suction effortupon the surrounding gas which lies against the inner face of the head10 and draws this partially saturated hot gas into the jet enteringthrough port 11 and into the dense area of the nebula.

The chilled and saturated gas thus forms a central downwardly flowingcolumn,

which cones outward at its lower end and escapes below the lower marginof the dr ing chamber to the exit compartment 5. Tlie surrounding lesschilled and unsaturated gas is caused to flow upward and to re-enter thedensest area of the nebula, where its useful .heat' is given up in theabsorption of moisture. A marked increase in eflicienc results by reasonof the fact that practically only moisture saturated gas escapes thedryin chamber. Per heat unit for a given volume of incoming hot gas, agreater volume of moisture is extracted from the nebula, before the gasescapes from the drying chamber.

While I have referred to the air currents as saturated and unsaturated,it will be understood that these words are not used in their technicallyexact sense, but to express their relative moisture laden andtemperature conditions. Similarly, while the term nebula is also used,it is intended to indicate merely a finely divided condition of theliquid under treatment. I

While I have mentioned onl the fundamental results flowing from t isconstruction and operation, various modifications will readily occur tothose dealing with the problem. Thus I have shown small ports 12 openingthrough the drying chamber wall just below the head 10. The hot airentering therethrough mingles with the rising gas and not only increasesits temperature, but aids the jet action of the gas entering at port 10in causing the unsaturated .gas to lfi-fil'ltel the nebula in itsdensest area The solids fall from the drying zone upon the floor 13 ofthe casing and are recovered in any suitable fashion. For example, theymay be swept by rake 14 into a chute 15 which delivers to a hopper, orbagging apparatus, or to further treating apparatus, as

maiy be desired. ith the understanding that onl a typical layout andoperation are descri ed to illustrate the thoughts whichv underlie myinvention, I claim 1. The method of spray drying which comprisesdispersing a fluid as a nebula, causin a convection current to traversethe zone 0 said nebula, leading the chilled and moisture saturatedportion of the convection current from the lower end of the. dryingchamber, and causing the unsaturated portion of the convection currentto rise and to re-enter the nebula zone to there absorb furthermoisture.

2-. The method ofspray drying which comprises dispersing a fluid as anebula, causing a convection current to traverse the zone of saidnebula, leading the chilled and moisture saturated portion of theconvection current from the lower end of the drying chamber, and causingthe upward flow of the unsaturated portion of the convection current bybringing it-into contact with a heated wall of the drying chamber.

3. The method of spray drying which comprises dispersing a fluid as anebula, causin a convection current to traverse the zone 0 said nebula,leading the chilled and moisture saturated portion of the convectioncurrent from the lower end of the drying chamber, and causing theunsaturated portion of the convection current to rise and to re-enterthe nebula zone to there absorb further moisture, the convection currentbeing concentrated upon the central area of the nebula zone as saidcurrent enters the dryin chamber.

4. The method of spray drying which comprises dispersing a fluid as anebula, causing a convection current to traverse the zone of saidnebula, leading the chilled and moisture saturated portion of theconvection current from the lower end of the dry ing chamber, andcausing the unsaturated portion of the convection current to rise and tore-enter the nebula zone to there absorb further moisture, andaugmenting the rise and return of the unsaturated portion of theconvection current to the nebula zone by the jet action of the incomingconvection current.

5. The method of spray drying which comprises dispersing a fluid as anebula, causing a convection current to traverse the zone of saidnebula, leading the chilled and moisture saturated portion of theconvection current from the lower end of the drying chamber, and causingthe unsaturated portion of the convection current to rise and tore-enter the nebula zone to there absorb further moisture, and augmentinthe return of the unsaturated portion o the convection current by theentraining action of auxiliary hot air jets converging upon the sprayzone.

6. A spray-drying apparatus comprising a tubular drying chamber having arestricted top opening, means for dispersing liquid from a point beneathsaid opening to form a nebula zone of greatest density directly beneathsaid opening, means for leading a convection current into the dryingchamber through said restricted opening, means for leading ofi moistentrained gas from the lower portion of the chamber, and means forrecovering solids deposited out of the liquid.

7. A spray-drying apparatus comprising a tubular drying chamber having arestricted top opening, the top of the drying chamber being inwardlydished to said opening, means for dispersing li uid from a point beneathsaid opening to orm a nebula zone of greatest density directly beneathsaid opening, means for leading a convection current into the dryingchamber through said restricted opening, means for leading off moistentrained gas from the lower portion of the chamber, and means forrecovering solids deposited out of the liquid.

8. A spray-drying apparatus comprising a tubular drying chamber having arestricted top opening, means for dispersing liquid from a point beneathsaid opening to form a nebula zone of greatest density directly beneathsaid opening, means for "leading a convection current into the dryingchamber through said restricted opening, means for leading off moistentrained gas from the into the drying chamber through said restrictedopening, means for leading ofl? moist entrained gas from the lowerportion of the chamber, and means for. recovering solids deposited outof the liquid. 10. A spray-drying apparatus comprising a tubular dryingchamber having a restricted top opening, ports formed in the wall of thedrying chamber adjacentthe dished top, means for dispersing liquid froma point beneath said opening to form a nebula zone of greatest densitydirectly beneath said opening, 'means for leading a convection currentinto the drying chamber through-said restricted opening, means forleading off moist entrained gas from the lower portion of thechamber,and means for. recovering solids deposited out of the liquid.

In testimony whereof I have signed my name to this specification.

' ARTHUR B. JONES.

